1. Field of the Invention
The present invention relates to a laser surveying system which comprises a rotational light emitting unit to rotationally emit a laser beam and a light receiving unit to receive the laser beam, to measure the position of the light receiving unit.
2. Description of the Related Art
For instance, Japanese Laid-open Patent Application Publication No. 2003-65762 discloses a rotational laser device for use in surveying for engineering works or the like, to rotationally irradiate a target with a laser beam and measure the tilt angle and height of the target relative to a plane orthogonal to a rotational axis according to a reflected light from the target.
Further, the use of a laser surveying system comprising a rotational light emitting unit and a light receiving unit to receive a laser beam from the rotational light emitting unit and measure a position relative to the rotational light emitting unit is known. This system can measure the angle of site and height of the rotational light emitting unit relative to the optical axis on the basis of a light receiving signal of the light receiving unit.
This rotational light emitting unit is comprised of a rotator rotatable around the axis relative to a case and a light emitting unit provided in the rotator to emit a certain laser beam. The rotational light emitting unit includes a ceiling covering above the rotator for the purpose of water resistance and protecting the rotator and the exit of the light emitting unit. The ceiling requires vertical columns in a space between the ceiling and the case to support the ceiling outside the rotator.
When the rotator is rotated relative to the case, a laser beam from the emitter may be partially blocked by the vertical columns while crossing them. This makes it difficult for the rotational light emitting unit to properly emit a laser beam in the positions of the columns in a rotational direction of the rotator. Accordingly, the laser surveying system including the rotational light emitting unit cannot accurately survey based on the light received by the light receiving unit which is blocked by the columns. In view of this, in this system a certain light shielding area in which the laser beam is partially blocked by the columns is preset in the rotational direction of the rotator so that the system does not perform surveying on the basis of a laser beam output from the light shielding area and received at the light receiving unit.
However, there is a problem that the light shielding area contains an area not blocked by the columns since it is set in accordance with a rotational position or rotational angle of the rotator about the rotational axis. Thus, the laser surveying system may not perform surveying on the basis of the laser beam received by the light receiving unit which has been properly emitted and not blocked by the columns, if the laser beam is in the light shielding area. This results in unnecessarily narrowing a proper surveying area.